An extensive post on the
Natural Selection Forums offers details on a bug they've been battling that
turns out to be present in the Half-Life source, rather than their mod. The
problem seems connected to client prediction where the final player on a full
server (i.e., player 10 on a 10-player server) is difficult to hit because the
visible character on screen is not in the same location as his hitbox. They have
determined that this problem is present in other (perhaps all) Half-Life mods,
though it is not clear if it appears in unmodified multiplayer games. The issue
also seems more evident the faster the bugged player is moving, which may be why
it was more obvious in Natural Selection games.

While this particular news isn't from Valve itself you gotta hand them that it's quite amazing how much they can get the newspapers to display their name on a daily basis even though they released their only commercial game Six freaking years ago.